Remediation of soil, sediment and other substrates (in the following text simply “soil”) by washing, extraction, leaching, and flushing (in the following text simply “washing”) with chelant is a process by which chelant (i.e. EDTA) and toxic metals form water-soluble complexes (chelates) and the washing solution is separated from the solid phase. However, toxic metals chelates with EDTA partly remain in washed soil. In the past, EDTA-based soil remediation has been compromised by extensive emissions of chelated toxic metals into the subsoil. In polluted soils, up to 20% of EDTA applied for remediation can be adsorbed into the soil, thereby leading to the risk of uncontrolled post-remedial leaching (Q. R. Zeng, S. Sauve S, H. E. Allen, W. H. Hendershot, Recycling EDTA solutions used to remediate metal-polluted soils, Environ. Pollut. 133 (2005), pp. 225-231). EDTA is characterized by low levels of biodegradability and high levels of environmental persistence (E. Bloem, S. Haneklaus, R. Haensch, E. Schung, EDTA application on agricultural soils affect microelement uptake of plants, Sci. Total Environ. 577 (2017), pp. 166-173). A 3-46% mineralization of 2-4 mg EDTA per kilogram of soil for the 13 surface soils after 15 weeks was documented (J. M. Tiedje, Influence of environmental parameters on EDTA biodegradation in soil and sediments, J. Environ. Qual. 6 (1997), pp. 21-26).
The patent application EP 3 153 246 A1 entitled “Soil and sediment remediation” of the same applicant describes a process wherein emissions of chelant and toxic metals is reduced with soil aging and remediated soil deposition on a reactive permeable barrier. The U.S. Pat. No. 5,965,024 entitled “Microbiological degradation of alkylene amine acetates” pertains to a process for the degradation of EDTA in waste waters under alkaline conditions but remains silent on EDTA degradation in EDTA-washed soil and sediment.
None of these known processes uses Fe and Fe-containing compounds to curb toxic emissions from soil, sediment or other substrate washed with chelant.